Quiet compiler warnings.
diff --git a/progs/samples/loadppm.c b/progs/samples/loadppm.c
index 5d3e3ab..b4b1b38 100644
--- a/progs/samples/loadppm.c
+++ b/progs/samples/loadppm.c
@@ -1,6 +1,6 @@
 
 typedef struct {
-    int sizeX, sizeY;
+    size_t sizeX, sizeY;
     GLubyte *data;
 } PPMImage;